The present invention relates generally to a method for remotely measuring the size of a dripping droplet, and specifically it relates to a method for detecting the dripping droplet which can preferably be applied to remotely and successively detect the leak of a liquid in a place inaccessible by a person, e.g. in a radiation environment, and to measure the leakage thereof accurately.
A prior art method has been known wherein a shadow of a dropping object formed when light from a light source is intercepted by the object is detected to remotely measure the size of the object.
One example of such a prior art method will be described in detail with reference to FIG. 8. In the state in which light emitted from a light source 1 is received constantly by a one-dimensional photosensor 3 such as a CCD (Charged Coupled Device of semiconductor) line sensor, the light is intercepted when a droppoing object 2, that is an object of detection, drops transversely between the light sensor 1 and the one-dimensional photosensor 3. FIG. 9 is a graph of the intensity of the light at that time which is detected as an electric signal by the one-dimensional photosensor 3, and the size of the object 2 can be measured from the width of a dark portion.
When the above-described prior art method is applied to detect a transparent object such as a dripping water droplet, however, a luminescent spot appears also in the central portion of an image due to the light transmitted through the transparent droplet as shown in FIG. 10, and consequently an electric signal is divided into two. As a result, there occurs a possibility that one object is detected as two. Moreover, since the light from the light source 1 is not parallel, it turns round along the object and reaches the one-dimensional photosensor 3, thus making the boundary of the dark portion (the shadow of the object) indistinct. In addition, the one-dimensional photosensor 3 receives the light from the light source 1 constantly and detects the shadow formed by the object, and therefore it detects the dark portion in bright light. Accordingly, a state that the electric signals are delivered constantly from the photosensor 3 constitutes the background, and this results in a fault of increased background noise.